In the treatment of oil bearing formations to stimulate oil production, one technique involves injection of water at high pressure into selected wells in the formation. The water desirably contains sand in selected proportions and in accordance with various other techniques, polymers or other chemicals are added to the water in liquid or solid form. The modified water is then delivered into the selected wells, preferably at elevated pressures.
Since sand is not soluble, the sand bearing water must be kept in a sufficient state of agitation during the course of its delivery into the formation, and must be initially agitated to create the desired suspension of sand in the water. Gelling agents, added as dry powders, are employed to increase the suspendability of the sand. Other dry powders, termed "polymers" are also often added to modify the water.
The dry chemicals, of whatever type, need to be readily and thoroughly wet and dispersed in the water to provide a uniform solution. One undesired effect of some prior methods of introducing dry powders into the water is the formation of agglomerates of dry chemical surrounded by a gelled mixture of water and powder, such agglomerates sometimes being referred to as "fish eyes". Such agglomerates are, of course, undesirable in the formation or in the well bore. In order to form good solutions or suspensions of dry chemicals, is desirable to introduce them into zones of high turbulence, low pressure, and high shear in the water.
In the delivery of water into a tank for mixing sand and chemicals into it, it is desirable to be able to separately influence the flow rate, delivery pressure, and linear velocity of the incoming water, in order to optimize the mixing conditions in the mixing vessel. Particularly, it is desirable to be able to independently control volumetric flow rate and linear velocity, since field applications may require widely varying volumetric flow rates, while a fairly narrow range of linear velocities is optimum for carrying out the mixing function.